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Horse gastrointestinal myiasis caused by larvae of Gasterophilus spp.has a worldwide distribution;however,little information is available on the genetic variation of Gasterophilus spp.in mitochondrial DNA(mtDNA)genes.In the present study,genetic variation was examined in three mtDNA genes,namely cox1,nad5 and rrnL,among G.intestinalis isolates originating from China.The complete cox1,had5 and rrnL gene sequences were amplified by PCR separately from adult G.intestinalis individuals and the amplicons were subjected to sequencing from both directions.The size of the sequences of cox1,had5 and rrnL gene was 1539 bp,1717 bp,and 1321 bp,respectively.The A+T contents of the sequences were 62.7-63.9%(cox1),70-70.7%(nad5)and 74.5-74.9%(rrnL).The intra-specific sequence variations within G.intestinalis were 0.1-3.1%for cox1,0.4-3.4%for nad5 and 0.1-1.5%for rrnL.Phylogenetic analyses using sequences of pcox1 with Bayesian inference indicated that all of the G.intestinalis isolates grouped together with high statistical support.These findings demonstrated the existence of intra-specific variation in mtDNA sequences among G.intestinalis isolates from China have implications for studying molecular epidemiology and population genetics of G.intestinalis.